Place sausage in a large skillet. Cook, stirring occasionally, until sausage is browned. Crumble and let cool slightly.
In a large bowl, whisk together the eggs, milk, salt, and dry mustard. Stir in the cheese.
Place the bread cubes in the prepared dish, followed by the sausage. Pour the egg mixture over the top. Gently press the bread cubes with your hands or a spatula so that they are covered by the egg mixture.
Refrigerate overnight, or for at least 2 hours.
Preheat oven to 350°F. Bake for 45 minutes, or until the casserole is cooked through.
Let cool for 5 minutes and serve.
Notes
If you don't have dry mustard, you can substitute 1 tablespoon of yellow mustard or Dijon mustard in its place.To freeze, place a double layer of foil over the UNCOOKED casserole and freeze for up to 1 month. Defrost in the refrigerator for 24 hours, remove the foil, and then bake as directed.